The present invention generally relates to an automatic focus control system for a photographic camera, and more particularly, to a focus condition detecting arrangement for use in an automatic focus control system.
Conventionally, there has been proposed, for example, in Japanese Patent Laid-open Application Tokkaisho No. 58-59413, a focus condition detecting device which is so arranged as to generate a focus condition detection signal indicative of amount and direction of deviation of an image of a target object from a predetermined focal plane based on output signals of AF (automatic focusing) photo-sensor arrays which detect an infrared light and a visible light from the target object as a mixed light. For compensation for the amount of deviation between an in-focus position by the infrared light and that by the visible light, the focus condition detection signal is corrected by the ratio in light amount of the visible light to the infrared light contained in the mixed light.
The known arrangement as described above, however, has such a disadvantage that the focus condition detection signal tends to be over-corrected with respect to a target object which has a high contrast, but is dark in the visible light region, or a target object having a low contrast, but bright in the infrared light region.